Comment on “Stratospheric Aerosol Composition Observed by the Atmospheric Chemistry Experiment Following the 2019 Raikoke Eruption” by Boone et al.

Based on satellite observations in the Arctic stratosphere at latitudes from 61° to 66°N in the second half of 2019, Boone et al. (2022, https://doi.org/10.1029/2022jd036600) provide the impression that the aerosol in the upper troposphere and lower stratosphere (UTLS) over the entire Arctic consisted of sulfate aerosol originating from the Raikoke volcanic eruption in the summer of 2019. Here, we show that this was most probably not the case and the aerosol layering conditions were much more complex. By combining the stratospheric aerosol typing results of Boone et al. (2022, https://doi.org/10.1029/2022jd036600) with lidar observations at 85°–86°N of Ohneiser et al. (2021, https://doi.org/10.5194/acp-21-15783-2021) of a dominating wildfire smoke layer in the UTLS height range, we demonstrate that the Arctic UTLS aerosol most likely consisted of Siberian wildfire smoke in the lower part and sulfate aerosol in the upper part of the aerosol layer which extended from 7 to 19 km height and was well observable until May 2020. The smoke- and sulfate-related aerosol optical thickness (AOT) fractions were about 0.7–0.8 and 0.2–0.3, respectively, according to our analysis. The sulfate AOT is in good agreement with model-based predictions of the Raikoke sulfate AOT.